1. Field of the Invention
The present invention relates to automatic slack adjusters, preferably of the single acting clearance or force sense sensing type, for disc brakes and in particular relates to improved single acting automatic slack adjusters for disc brakes wherein means are provided to prevent the coil return springs from being torsioned (i.e. wound up) during the adjustment operation which might result in an undesirable rotation of the adjusting mechanism as the return spring later unwinds.
2. Brief Description of the Prior Art
Automatic slack adjusters for railway brakes and automative brakes of both the disc and drum type are well known. In particular, automatic, single acting (i.e. operates automatically in the slack take-up direction only) vehicle slack adjusters of the force sensing type (also called the clearance sensing type) wherein the adjustment mechanism will sense the forces in the brake system and either disengage the adjustment mechanism or slip when forces exceed a predetermined level, usually corresponding to the expected forces in the system when the drums or discs are contacted by the movable friction elements, to prevent over adjustment are well known and may be appreciated in greater detail by reference to U.S. Pat. Nos. RE 26,965 and 3,507,369, both of which are hereby incorporated by reference. Clearance sensing slack adjusters wherein a torque limited friction clutch of the coil slip clutch type is utilized to limit torque applied to an adjustment member are also known as may be seen by reference to U.S. Pat. Nos. 3,507,369 and 3,901,357, both of which are hereby incorporated by reference.
Automatic slack adjusters for disc brakes wherein a rod carrying a friction pad, or a slidable caliper pressure plate, is threadably attached to an adjustment nut member, and slack is maintained within predetermined limits by selective relative rotation of the adjustment nut member and rod are known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,966,028 and 4,064,973, both hereby incorporated by reference.
While the automatic clearance sensing disc brake slack adjusters of the prior art have been generally well received, certain of the prior art devices were not totally satisfactory as rotation of the rotatable adjustment member tended to torque (i.e. wind-up) the brake coil return spring, which return spring tended to unwind in a manner causing the rotatable adjustment member to be undesirably rotated in the slack increasing direction of rotation.